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Thursday, April 01, 2004

Why Australia's soil + drinking water are going salty...
The latest edition of BBC Radio 4's Costing the Earth programme investigates the threat posed by dryland salinity to Australia's most productive farmlands + drinking water.

Dryland salinity is caused by a combination of ancient + modern events.

In prehistoric times, the tectonic plate that was to become Australia was located under the sea.

When this plate was eventually lifted above sea-level, salt deposits and evaporation, formed a salt crust that was, only very slowly, washed underground, by many millions of years of rain...

More recently, over the last 200 years, and especially the last 50 years, vast areas of Australia have been cleared for agriculture...

The consequent loss of big trees (which drank, and then sweated large quantities of water, into the air, through their leaves), and their replacement with less thirsty grasses, such as wheat or pasture (which do not), has resulted in water tables, across Australia, being pulled towards the surface, by the heat of the sun.

Unable to escape into the air, this water has started to pool around soil particles close to the surface and, once here, steadily pulled up salts from deep underground (a bit like wet tissue paper soaks up ink).

Gradually, the concentration of salts at the surface has increased and, in more and more places, produced lifeless salt pans... It is almost impossible for most plants to live, or for animals to find untainted water, on such hyper-salty soils. As a consequence, millions of acres of formerly productive land have been turned into lifeless desert.

Unfortunately, it is not just the country people and wildlife that suffer from the impacts of this problem...

Country streams, draining from salty land, eventually flow into rivers which then supply most of Australia's major cities with their drinking water...

Food production, which is already difficult in semi-arid areas, and generally expected to increase, has also become impossible in previously fertile areas, and even native plants, which evolved while areas were salt-free, are unable to survive.

The threat posed by salinity is immense, and this programme does a good job of looking at what the problems are and what can be done to tackle them...